1. Field of the Invention
The present invention relates to a vehicular air-conditioner provided with a function of protection of a cooling system using an electric compressor.
2. Description of the Related Art
Known in the past has been a vehicular air-conditioner using an electric compressor, provided with a compressor body for suction and discharge of a refrigerant, a compression unit for compressing the refrigerant sucked into the compressor body, an electric motor for driving the compression unit, and a motor drive device for driving and controlling the electric motor, for a refrigeration cycle provided with a condenser, pressure reducer, evaporator, etc.
In such a vehicular air-conditioner, the motor drive device for driving and controlling the electric compressor becomes high in temperature due to the heat generated along with operation of the motor drive device itself and the heat exhausted from the engine and other heat sources. Due to this, a motor drive device provided with a semiconductor device is liable to stop functioning normally. To deal with this, one practice has been to arrange the motor drive device at a position enabling heat exchange with the refrigerant at the suction side of the electric compressor and raise the speed of the electric motor to increase the amount of suction of the refrigerant in the electric compressor and thereby cool the motor drive device when the temperature of the motor drive device exceeds a predetermined value so as to thereby protect the motor drive device against heat (for example, see Japanese Unexamined Patent Publication (Kokai) No. 2003-139069). However, the above related art did not consider protection of the motor drive device against heat when the electric motor of the electric compressor stopped, that is, when no refrigerant was flowing.
Further, when the electric motor was stopped or the cooling heat load was small, that is, when there was almost no heat exchange at the heat exchange means in the refrigeration cycle comprised by the condenser and evaporator, the following problems arose when trying to protect the motor drive device from heat by increasing the speed of the electric motor to forcibly make the refrigerant flow in the refrigeration cycle.
That is, if trying to supply high pressure refrigerant to a condenser not engaged in almost any heat exchange, the flow rate of the refrigerant at the condenser does not sufficiently rise, so the pressure at the refrigerant introduction port side of the condenser increases and the torque of the electric motor increases correspondingly. Due to this, the current of the electric motor also increases, so a rise in the internal temperature of the motor drive device is invited and a sufficient cooling effect by the refrigerant of the motor drive device can no longer be obtained. Further, if trying to supply high pressure refrigerant to the condenser, the pressure at the refrigerant introduction port side of the condenser excessively increases and the pressure is liable to damage the refrigerant flow passage and cause the refrigeration cycle to stop functioning.
On the other hand, even at the evaporator, since the amount of heat exchange is low, an increase in the flow rate of the refrigerant to the evaporator causes the evaporator to be excessively cooled and water of condensation of the condenser to freeze (forming frost). Due to this as well, the refrigeration cycle is liable to stop functioning.